Regulation of ornithine decarboxylase gene expression in normal and transformed hamster embryo fibroblasts following stimulation by 12-O-tetradecanoylphorbol-13-acetate

We have compared the regulation of ornithine decarboxylase (ODC)gene expression in primary cultures of hamster embryo fibroblastsand in two independently transfonned hamster embryo cell lines.Previous studies have demonstrated that 12-O-tetradecanoylphorbol-13-acetate(TPA) can greatly potentiate the serum growth factor inductionof ODC enzyme activity in transformed cells, but not in normalhamster embryo fibroblasts. Treatment of either normal or transformedcells with both TPA and serum yielded greater accumulationsof ODC mRNA than with either treatment alone, which is consistentwith changes at the protein level. However, treatment of thetransformed cells with TPA and serum resulted in a greater increasein steady state levels of ODC mRNA than that observed usingnormal fibroblasts. The time course for the induction of ODCmRNA was similar for both normal and transformed cells withmaximal accumulations 4–8 h after treatment. Studies withactinomycin D further suggests that ODC mRNA is comparativelylong-lived in both normal and transformed cells. The accumulationof ODC mRNA after stimulation with TPA and serum is blockedby cycloheximide in normal hamster fibroblasts suggesting thatthis induction is dependent upon protein synthesis. In contrast,cydoheximide did not affect the accumulation of ODC mRNA undersimilar treatment conditions in transformed cells. This alteredregulation of ODC gene expression in transformed hamster embryofibroblasts cannot be explained by either gene rearrangementor the amplification of an ODC gene. These data suggest thattransformation of hamster embryo cells results in a loss ofcellular control over ODC gene regulation which includes analteration in the requirement for protein synthesis for ODCmRNA accumulation.